The present invention relates to a reduction resistive dielectric ceramic composition containing therein ceramic grains of a core-cell structure and a ceramic capacitor including therein dielectric layers made by using such a ceramic composition.
Recently, a base metal, e.g., Ni, has been widely used in forming internal electrodes of a multilayer ceramic capacitor for the purpose of reducing manufacturing costs and various reduction resistive dielectric ceramic compositions capable of being sintered simultaneously with the internal electrodes composed of the base metal have been developed. One of the reduction resistive dielectric ceramic compositions is a barium titanate-based dielectric ceramic composition including ceramic grains of a core-shell structure.
However, in case where a multilayer ceramic capacitor, which fulfilled the X7R characteristic (EIA standards) or the B characteristic (EIAJ standards), is manufactured by employing a barium titanate-based dielectric ceramic composition having a dielectric constant equal to or greater than 3000 and internal electrodes composed of the base metal, such as Ni, capacitance aging become deteriorated.
It is, therefore, an object of the present invention to provide a multilayer ceramic capacitor yielding a maximum temporal capacitance variation not smaller than xe2x88x9230% with a voltage bias of 2 V/xcexcm, even when a dielectric ceramic composition having a dielectric constant (∈) of greater than 3000 and a good reduction resistance to is used.
In accordance with one aspect of the present invention, there is provided a dielectric ceramic composition including: sintered ceramic grains having a core-shell structure, wherein smaller than or equal to 50% of the grains have a domain width of twin less than 20 nm; 30% to 70% of the grains have a domain width of twin in the range from 20 nm to 50 nm; less than or equal to 50% of the grains have a domain width of twin greater than 50 nm or have no twin.
In accordance with another aspect of the present invention, there is provided. a ceramic capacitor including more than one internal electrodes; and one or more dielectric layers composed of a dielectric ceramic composition, each of the dielectric layers being sandwiched between two neighboring internal electrodes, wherein the dielectric ceramic composition includes sintered ceramic grains having a core-shell structure, wherein smaller than or equal to 50% of the grains have a domain width of twin less than 20 nm; 30% to 70% of the grains have a domain width of twin in the range from 20 nm to 50 nm; less than or equal to 50% of the grains have a domain width of twin greater than 50 nm or have no twin.